Tuesday - June 30
Today we discussed the Chrom-Agar, which we use to plate urines on. This helps to rapidly identify or at least narrow down what the organism may potentially be. For instance, two plates usually come with a urine culture, a SB (sheep blood) and the Chrom-Agar. Because of the amount of testing that the Microbiology lab undertakes, those two plates may not make it to the Urine bench at the same time. If you have the sheep blood, you could make a quick deduction that would further lead you to understand what potential pathogen(s)/ normal flora may be present. An example lies within distinguishing between gram negative and gram positive bacteria. Gram positive colonies on a SB plate are usually small and non-mucoid, whereas the gram negative bacteria are larger, more spready or mucoid. When you look at the chom-agar, E.coli appears pink. So do a few other gram positive organisms, such as S. saprophyticus. However, having the sheep blood allows you to do a quick sweep catalase if needed, or colony morphology can be very decisive. If the SB plate does not make it with the chrom-agar, it is very easy to look at the plate and almost know, without any other reference, what is growing upon that specific plate. Gram staining is always used for clinical application, as well as simple tests such as oxidase and catalase. From there, organisms are counted for CFU/ml. If an organism has over 100 CFU/ml, we know that there is an infection, and our work up then travels to the susceptibility bench, after we have the bug isolated.
We also discussed policies and procedures as we began reviewing more CF plates as well as other samples. Pesudomonas aeruginosa, as I have reflected upon many times before, can present with so many strains that differentiating can be very difficult. We were also given the chance to observe the plates without previous deduction, and asked to identify the organisms upon sight. This proved to be unnerving. I felt uncomfortable just making a judgement without any further testing - luckily, further testing is only a drop of hydrogen peroxide away. I really appreciated the insight that our teaching instructors in the lab gave us today.
Wednesday - July 1
Today was very interesting; my teaching instructor thought I had swine flu. Thus, I don’t remember much of what happened. I distinctly remember being frustrated with the “review” that was given, but I deviate. Wednesday was fascinating when we plated in the afternoon. So many different sample types were presented to us within in the hour that I felt as though my technique greatly improved. We plated BAL samples, pleural fluid, respiratory samples searching for Legionella, wound samples searching for anaerobic organisms, sputum (most likely a CF patient), throat (I despise getting my throat swabbed, as did our instructor, so she told us to be extra sensitive - I thought that was nice), NP (nasopharyngeal) culture searching for Pertussis (as in Bordatella pertussis), and a CSF culture. I watched how much the instructor had to know immediately upon receiving the sample. Conveniently, cards with the standard procedure are provided to double check.
Again, we sat upon the bench, and this time did some gram staining. Another specialist was adamant that we compare pure isolates of certain bugs under the microscope - its easy to think that gram negative cocci, such as Moraxella catarrhalis and Strep. pneumoniae appear similar, but upon closer examination, the S. pneumoniae appears lancet shaped - often, they can also be confused with Enterococcus. We reviewed more plates from CF patients and reference samples, helping us to become increasingly more familiar with the process. We also reviewed more procedures as we did the plate exercise.
Thursday - July 2
An exam filled the first hour or so of the morning. Then, it was back to the lab to review more bench samples. A favorite part of today was when we were able to retrieve the samples that had been plated the day before and review them with the bench tech. All of a sudden, and for the first time, we were actually being instructed. It was as though a light shone down upon our little section in the lab and enlightenment came to be. We were able to look the the plates individually alongside the resident expert. This was so rewarding. I isolated this beautiful example of Beta-Strep and when the medical residents came around, they took my plate to instruct the doctors upon the appearance and clinical significance of Beta-Strep. Our resident tech was very helpful is assisting us with differentiating colonies as well as grading our isolation. I was very appreciative and felt as though microbiology was manageable after all.
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